This invention relates to a fluid displacement apparatus, and more particularly, to a fluid displacement apparatus of the scroll type.
Scroll type apparatus are well known in the prior art. For example, U.S. Pat. No. 801,182 discloses a device including two scroll members each having a circular end plate and a spiroidal or involute spiral element. These scroll members are maintained angularly and radially offset so that both spiral elements interfit to make a plurality of line contacts between their spiral curved surfaces, thereby to seal off and define at least one pair of fluid pockets. The relative orbital motion of the two scroll members shifts the line contact along the spiral curved surfaces and, therefore, the fluid pockets change in volume. The volume of the fluid pockets increases or decreases dependent on the direction of the orbiting motion. Therefore, the scroll type apparatus is applicable to compress, expand or pump fluids.
In comparison with conventional compressors of the piston type, the scroll type compressor has certain advantages, such as fewer parts and continuous compression of fluid. However, there have been several problems, primarily the sealing of the fluid pockets. Sealing of the fluid pockets must be sufficiently maintained in a scroll type fluid displacement apparatus, because the fluid pockets are defined by the line contacts between the interfitting spiral elements and axial contacts between the axial end surfaces of the spiral elements and the inner surfaces of the end plates.
One solution to the sealing problem, in particular, that relating to axial sealing, is described in U.S. Pat. No. 3,874,827. This patent discloses the concept of non-rotatably supporting the fixed scroll member within the compressor housing in an axially floating condition. A high pressure fluid is introduced behind the fixed scroll member to establish sufficient axial sealing. In this arrangement, since the fixed scroll member is supported in an axially floating condition, the fixed scroll member may wobble due to the eccentric orbital motion of the orbiting scroll member. Therefore, sealing and resultant fluid compression tends to be imperfectly performed.
In order to avoid these disadvantages, the pressure of the high pressure fluid introduced must be increased, and the clearance between radial supporting parts must be made as small as possible. However, costly close tolerances of the working parts is required to minimize this clearance, while an increase of the pressure of the introduced fluid results in increased contact pressure between both scroll members, which increases mechanical loss or may damage them.
Another method for improving the axial seal of the fluid pockets is to use seal elements which are mounted in the axial end surface of each of the spiral elements, as disclosed in U.S. Pat. No. 3,994,635. In this arrangement, the end surface of each spiral element facing the end plate of the other scroll member is provided with a groove formed along the spiral. A seal element is placed within each of the grooves. An axial force urging means in each groove, such as a spring, urges the seal toward the facing end surface of the end plate to thereby effect axial sealing. In this arrangement, the construction for the axial force urging means for the seal is complex, and it is difficult to obtain the desired uniform sealing force along the length of the seal element.
In order to avoid these disadvantages, the seal element is loosely fitted into the groove formed in the axial end surface of each spiral element, and the pressurized fluid is introduced into the groove from adjacent fluid pockets to urge the seal element towards the facing end plate, as a substitute for mechanical urging means, to thereby effect axial sealing. However, the seal element is subject to localized excessive wear during a portion of the orbital motion of the orbiting scroll member. That is, during the period when the pair of fluid pockets are both connected to the central high pressure space, localized fluid pressure behind the seal element is suddenly enlarged, resulting in excessive sealing force which sometimes induces localized bending of the seal element and excessive sealing force.